In recent years, crystalline silicon photovoltaic elements using a monocrystalline silicon substrate or a polycrystalline silicon substrate (simply referred to as photovoltaic elements in some cases below) are being vigorously developed. Especially, those using the monocrystalline silicon substrate are excellent in photoelectric conversion efficiency, and are spreading as the price of silicon wafers is lowered. For some usage such as urban housing with a limited installation space, it is required to further improve the photoelectric conversion efficiency.
One of methods for improving the conversion efficiency of the crystalline silicon photovoltaic elements is a back contact (back face juncture) cell, in which electrodes blocking light are not formed on a light receiving face, but are formed on the back only. Because of its high light utilization efficiency, the back contact cell is excellent in the photoelectric conversion efficiency, and is already used widely in practice.
On the other hand, a heterojunction cell which is a combination of the crystalline silicon substrate and an amorphous silicon thin film has an open circuit voltage higher than those of general crystalline silicon photovoltaic elements to have higher photoelectric conversion efficiency. Because the amorphous silicon thin film is formed on the crystalline silicon substrate, the heterojunction cell is a technique also referred to as hybrid.
Then, proposed is a back contact heterojunction photovoltaic element which is a combination of these techniques (for example, refer to Patent Document 1). Its detailed configuration is that on the back of a monocrystalline silicon substrate, an i-type amorphous silicon film is formed, on which a p-type amorphous silicon film, a back electrode and a collector electrode are formed for serving as a positive electrode, and on which an n-type amorphous silicon film, a back electrode and a collector electrode are formed for serving as a negative electrode.